Thin film deposition is used to build materials by in essence growing material on a surface, commonly a substrate. These materials have many uses in microelectronics as well as in other fields. Two well known thin film deposition techniques are Atomic layer deposition (ALD) and Chemical Vapor Deposition (CVD). In each technique, reactants, i.e. precursors often in the form of gasses, are fed into a reactor which over a period of time forms a desired material.
During normal operation of Atomic Layer Deposition (ALD) reactors, two or more reactants are alternatingly introduced to the reactor. For ideal operation, the switching of gases in the reactor should be as fast and thorough as possible. This makes ALD inherently slow as purging gas volumes is slow and difficult.
Chemical Vapor deposition (CVD) is based on the continuous flow of a precursor/precursors to the reactor. Thus, the growth per minute of CVD is generally higher than that in ALD. Due to different requirements for the ALD and CVD reactors, a CVD reactor historically cannot typically be easily used for ALD growth of films successfully.
For example, in typical ALD reactors the gas volume in the reactor should be as small as possible. In CVD reactors, the accurate and uniform concentration distribution over the substrate is a typical design criterion. For CVD reactors, said accurate and uniform concentration distribution is more important than the low volume required by ALD designed reactors.
Source delivery principles are also very different when comparing typical ALD and CVD reactors. In ALD reactors, it is desirable for the injection of a concentrated precursor pulse to occur quickly along with the subsequent fast and thorough purging of the flow channel. To the contrary, in CVD, the steady and controllable partial pressure flux from the source is the most important design factor.
Because CVD is older than ALD, CVD reactor geometry has been optimized for the past several decades and is a considerably mature technology. Therefore, it would be very desirable if current CVD reactors could be modified to function more, or entirely in an ALD mode.